Season the chicken breast on both sides with sea salt, black pepper, and dried oregano.
Heat 0.5 tbsp of olive oil in a skillet over medium-high heat until shimmering.
Cook the chicken for 6-7 minutes per side until golden brown and the internal temperature reaches 165°F.
In a small bowl, whisk the remaining 0.5 tbsp of olive oil with the fresh lemon juice and Dijon mustard to make the dressing.
Slice the cucumber into half-moons, halve the cherry tomatoes, and cut the avocado into thin wedges.
Allow the chicken to rest for 3 minutes after cooking, then slice it into thin strips.
Place the mixed baby greens in a large bowl and toss with the prepared lemon-herb dressing.
Top the greens with the sliced chicken, cucumber, cherry tomatoes, and avocado wedges before serving.